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Deuterium NMR methods are used to characterize the dynamic structure of PPTA [poly-(p-phenyleneterephthalamide)] fiber as a function of tension. Spin-lattice relaxation results indicate that the high-frequency component of the dynamic structure is not significantly altered by the fiberspinning process or by the application of tensile stress to the fiber and as such does not differ from that of the as-polymerized polymer. Quadrupolar-echo line shapes reflect the high degree of order as well as the motional heterogeneity of the fiber bundle. The application of a tensile stress equivalent to 55% of the breaking strength of the fiber bundle alters the 2H NMR line shape, thus reflecting the coupling of macroscopic stress and microscopic dynamic structure through the enhancement of the phenylene ring dynamics. Two-dimensional 2H NMR methods are used to characterize the chain axis orientational distribution of a continuous fiber bundle. Simulations of the experimental spectra are consistent with a Gaussian distribution of orientations with a standard deviation of no larger than 5°; this result is in good agreement with previous X-ray results and differs substantially from previous solid-state NMR approaches which utilized chopped fibers.

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